1. Technical Field of the Invention
This invention relates to methods of forming a reflecting mirror and a reflecting face, for a vehicle head lamp, to provide a downward-beam light distribution.
2. Related Art
In a basic configuration, a vehicle head lamp includes a reflecting mirror shaped like a paraboloid of revolution and a front lens having a diffusing lens ahead the reflecting mirror. Recently, the light distribution control function has been at least partially shifted from the front lens to the reflecting mirror so that the front lens can be slanted so as to match the shape of a particular vehicle. That is, the lens is slantedlargely in a vertical plane to match the shape of a front end of a car body and, thereby, provide a lamp shape suitable for the vehicle shape. However, to maintain a suitable light distribution as required for each car model, the full face of a reflector is used effectively, whereby a light distribution pattern having a cutoff line peculiar to a downward beam can be formed is proposed; for example, a lamp disclosed in U.S. Pat. No. 5,258,897, etc., is known.
That is, in this kind of lamp, the front lens becomes plain, or nearly plain so that very little lens step is formed. thus, the curved surface design of the reflecting mirror is important in determining the light distribution spread of the lamp.
1. Problems to be Solved by the Invention
To form a slant cutoff line peculiar to a downward-beam light distribution (15-degree slant) in vehicle illumination, it is not easy to provide a sufficient amount of light to a long-distance area or a medium-distance area positioned just below the line with the related-art reflecting mirror. Thus, there is a risk of hindering improved visibility on the line of the vehicle having the reflecting mirror.
It is therefore an object of the invention to design a curved reflecting surface which provides a sufficient amount of applied light in the range near a slant cutoff line in a downward-beam light distribution, thereby improving visibility in a long-distance region and a medium-distance region.
2. Means for Solving the Problem
The present invention is based on the premise that the basic reflecting face satisfies the following three requirements (a to c) to provide a light distribution pattern of a downward-beam having a slant cutoff line inclined with respect to a horizontal direction:
(a) A curve set in a horizontal reference face containing an optical axis, or a curve set in a slant reference face inclinedxe2x80x94at a predetermined angle with the optical axis used as an axis of rotationxe2x80x94with respect to the horizontal reference face, is used as a reference curve;
(b) A light source body has a center axis extended along the optical axis and is placed near a reference point of the reference curve; and
(c) The reflecting face is formed as a set of cross lines provided by cutting a virtual paraboloid of revolution having an axis parallel with a light beam vector of reflected light when light assumed to be emitted from the reference point of the reference curve positioned on the optical axis is reflected at an arbitrary point on the reference curve, wherein the paraboloid passes through the reflection point, and has the reference point as a focus on a virtual plane which contains the light beam vector and is parallel with a plane orthogonal with or inclined to the horizontal reference face or the slant reference face.
For a first reflecting area, close to the horizontal reference face when the reflecting face is viewed from the optical axis direction, a reference curve is set in a slant reference face inclined to the horizontal reference face at a first angle equal to the angle of the slant cutoff line with a horizontal line. Further, for a second reflecting area, positioned above or below the first reflecting area with respect to the horizontal reference face when the reflecting face is viewed from the optical axis direction, a reference curve is set in a slant reference face inclined to the horizontal reference face at a second angle larger than 0xc2x0 and smaller than the angle of the slant cutoff line with the horizontal line.
Therefore, according to the invention, the projected image of the light source body provided by the first reflecting area is placed along the slant cutoff line just below the slant cutoff line, whereby a necessary amount of light is provided for distant forward visibility on the lane of the vehicle containing the head lamp. The projected image of the light source body provided by the second reflecting area is placed along a line having an angle smaller than the slant cutoff line, whereby an amount of light is provided to the medium-distance region forward on the lane of the vehicle containing the head lamp.